The present invention relates to a new and improved method and apparatus for removing moisture from pulp and more specifically to an apparatus which controls the moisture content of pulp discharged from a press.
Known waste material handling systems have included a pulper unit having a tank of water in which a wide range of solid waste materials have been macerated to form a slurry. The slurry of waste material is conducted to a press which removes water from the slurry to form a moist pulp which is discharged to a suitable container. Known systems which include a pulper unit and press are disclosed in U.S. Pat. Nos. 3,188,942; 3,191,872; 3,319,897; and 3,375,776. Various patents have also been obtained on specific water press constructions. Typical of these patents are U.S. Pat. Nos. 3,062,129; 3,426,677 and 3,688,687.
In these known presses, the moisture content of the pulp is controlled within a limited range by a restrictor member or compression cone. The restrictor cone is tightly clamped to a press screw drive shaft. The clamp which secures the cone to the drive shaft can be released to change the position of the restrictor cone along the shaft. This varies the compression which is applied to the pulp to thereby vary the moisture content of the pulp. Thus, if the pulp discharged from a press is too wet, the restrictor cone is adjusted downwardly toward the screw to increase the extent to which it restricts the outlet from the press to thereby increase the compression action applied against the pulp. Similarly, if the pulp which is discharged from the press is too dry, the restrictor cone is moved upwardly to decrease the extent to which it restricts the outlet of the press to thereby reduce the compression action applied against the pulp.
Even though an operator realizes that the position of the restrictor cone should be adjusted to accommodate pulp of different consistencies, most operators are reluctant to adjust the cone. This is because each readjustment of the restrictor cone requires cleaning out of the pulp from around the cone, removing or loosening set screws and handling the cone to position it along the drive shaft. Since the materials which are being processed by the press are waste materials and will frequently carry a foul odor, the idea of handling the material to clear out the restrictor cone and adjust the position of the cone is not attractive to most operators.
It is believed that most operators leave the cone in the position to which it is adjusted at a factory where the press is manufactured. The factory setting for the restrictor cone is sufficiently high to avoid having pulp which is too dry and to avoid overloading the press drive motor. However, when the restrictor cone is at the factory setting, the compressed pulp may contain excess moisture. In many instances, the press operator is not concerned if the pulp is overly damp. However, in order to maximize the operating efficienty of the press, the discharged pulp should have a moisture content of approximately 70%.
Difficulties can arise when an operator moves the restrictor cone downwardly from its factory setting and leaves the cone at the lower setting. This lower setting enables the press to efficiently squeeze water out of short fibered waste materials, such as table napkins and food waste. The difficulties arise when the restrictor cone is left at the lower setting and long fibered materials, such as corrugated boxes, are fed to the pulper and then to the press.
When the higher consistency pulp formed from long fibered waste materials is processed in a press in which the restrictor cone is too low, an overloading of the press drive motor can result. When this happens, the press jams and/or the electrical circuitry is overloaded and a fuse may be blown. When this occurs, it is necessary to clean out hard packed material at the top of the press screw by hand. Since the waste materials which are processed through the press frequently contain waste food and other substances, the hand cleaning of the press is not a particularly pleasant task.
In an effort to maintain the back pressure in a water press within predetermined limits, U.S. Pat. No. 3,394,649 suggests that hydraulic cylinders be provided to move a cylindrical screen relative to a screw. The hydraulic cylinders are activated to move the screen in response to variations in the current required to operate a press drive motor. The movement of the screen varies the press discharge area.